MXPA01009490A - Aqueous acrylic emulsion polymer composition. - Google Patents

Abstract

An aqueous acrylic emulsion polymer including, as copolymerized units, 70 to 99.5% by weight, based on dry polymer weight, monoethylenically unsaturated nonionic (meth)acrylic monomer and from 0.3 to 10% by weight, based on dry polymer weight, monoethylenically unsaturated acid monomer, wherein at least 40% by weight, based on dry polymer weight, of the emulsion polymer is formed by redox polymerization in the presence of 0.001 to 0.05 moles chain transfer agent per kg dry polymer weight is provided. An aqueous coating composition including the acrylic emulsion polymer and a method for improving the scrub resistance of a dry coating including applying the aqueous coating composition to a substrate; and drying, or allowing to dry, the aqueous coating composition are also provided.

Description

\ COMPOSITION OF POLYMER IN AQUEOUS ACRYLIC EMULSION This invention relates to an aqueous acrylic emulsion polymer, suitable for delivering dry coatings having improved scouring resistance. More particularly, the invention relates to an aqueous acrylic emulsion polymer which includes, as copolymerized units, from 70 to 99.5% by weight, based on the weight of the dry polymer, of a monoethylenically unsaturated (meth) acrylic monomer , and from 0.3 to 10% by weight, based on the weight of the dry polymer, of an acid monoethylenically unsaturated monomer, in which at least 40% by weight, based on the weight of the dry polymer, of the emulsion polymer , which is formed by the redox polymerization, in the presence of 0.001 to 0.05 moles of a chain transfer agent per kilogram of the dry polymer weight. The invention also relates to an aqueous coating composition that includes an acrylic emulsion polymer and to a method for improving the scrub resistance of a dry coating, which includes applying the aqueous coating composition to a substrate; and drying or allowing to dry, the aqueous coating composition.

The present invention serves to provide a dry coating, including a binder of an emulsion polymer, predominantly acrylic, of a certain composition, prepared by a certain process, said coating exhibits an improved resistance to scrubbing, by which it means here an improved strength to scrubbing relative to that of dry coatings incorporating an acrylic emulsion polymer binder not constituted in this manner, and concurrently providing a level of alkaline strength, suitable for use on alkaline substrates, such as masonry substrates. PCT Patent Application, WO 9918157, is directed to scrub-resistant latexes and discloses compositions prepared by a two-stage polymerization, in which a monomer effective in increasing the wet adhesion properties of the polymer in either or both is included. stages. Scour resistance is generally recognized as a desirable feature of a coating. The problem faced by the inventors is the provision of a suitable emulsion polymer, an aqueous coating composition and a method for improving the scrub resistance of a coating, so that a useful level of a scrub resistance can be realized. Alternative polymerization processes that are effective in achieving this end are desired. We have now found that certain polymer compositions in predominantly acrylic emulsion, prepared where at least 40% by weight, based on the weight of the polymer, of said emulsion polymer, is formed by the redox polymerization, in the presence of 0.001 a 0.05 moles of a chain transfer agent per kilogram of dry polymer provide useful levels of scrub resistance and adequate alkaline resistance. In a first aspect of the present invention, an aqueous acrylic emulsion polymer is provided, which includes, as copolymerized units, from 70 to 99.5% by weight, based on the weight of the dry polymer, of a non-ionic (meth) acrylic monomer , monoethylenically unsaturated and from 0.3 to 10% by weight, based on the weight of the dry polymer, of an acid monoethylenically unsaturated monomer, in which at least 40% by weight, based on the weight of the dry polymer, of the polymer in emulsion, it is formed by the redox polymerization, in the presence of 0.001 to 0.05, preferably 0.0026 to 0.025 moles of a chain transfer agent, per kilogram of the dry polymer weight. In a second aspect of the present invention, an aqueous coating composition is provided, which includes an aqueous acrylic emulsion polymer, this polymer includes, as copolymerized units, from 70 to 99.5% by weight, based on the weight of the dry polymer, of a non-ionic (meth) acrylic, monoethylenically unsaturated monomer and from 0.3 to 10% by weight, based on the weight of the dry polymer, of an acid monoethylenically unsaturated monomer, in which at least 40% by weight, based on the weight of the dry polymer, of the emulsion polymer, is formed by the redox polymerization, in the presence of 0.001 to 0.05, preferably 0.0025 to 0.025 moles of a chain transfer agent per kilogram of dry polymer weight. In a third aspect of the present invention, a method is provided for improving the scrub resistance of a dry coating, which includes: a) forming an aqueous coating composition, including an aqueous acrylic emulsion polymer, said polymer includes, as copolymerized units, from 70 to 99.5% by weight, based on the weight of the dry polymer, of a non-ionic (meth) acrylic, monoethylenically unsaturated monomer, and from 0.3 to 10% by weight, based on the weight of the dry polymer , of an acid monoethylenically unsaturated monomer, in which at least 40% by weight, based on the weight of the dry polymer, of the emulsion polymer, is formed by the redox polymerization, in the presence of 0.001 to 0.05, preferably 0.0025 to 0.025 moles of chain transfer agent per kilogram of dry polymer weight; b) applying the coating composition to a substrate; and c) drying, or allowing to dry, the applied coating composition. The aqueous acrylic emulsion polymer contains, as copolymerized units, from 70 to 99.5% by weight, based on the weight of the dry polymer, of a non-ionic, monoethylenically unsaturated, copolymerized (meth) acrylic monomer, including esters, amides and (meth) acrylic acid nitriles, such as, for example, (meth) acrylic ester monomers, including methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, acrylate lauryl, stearyl acrylate, methyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, aminoalkyl (meth) acrylate, N-alkyl-aminoalkyl (meth) acrylate, N, N-dialkyl (meth) acrylate -aminoalkyl; urieido (meth) acrylate; (meth) acrylonitrile and (meth) acrylamide. The use of the term "(met)" followed by a thermal one, such as acrylate, acrylonitrile or acrylamide, as used throughout the description, refers to both acrylate, acrylonitrile or acrylamide, and methacrylate, methacrylonitrile and methacrylamide, respectively. By "nonionic monomer" is meant here that the copolymerized monomer residue does not carry an ionic charge between pH 1 to 14. The aqueous emulsion polymer contains, as copolymerized units, from 0.3 to 10% by weight, based on the weight of the dry polymer, of a monoethylenically unsaturated acid monomer, such as, for example, acrylic acid, methacrylic acid, crotonic acid, l-itaconic acid, sulfoethyl methacrylate, phosphoethyl methacrylate, fumaric acid, maleic acid, monomethyl itaconate , monomethyl fumarate, monobutyl fumarate and maleic anhydride. Preferably, the emulsion polymer contains, as copolymerized units, 0.3 to 2.5% by weight, based on the weight of the dry polymer, the acid (met) acrylic. The aqueous emulsion polymer further contains, as copolymerized units, from 0 to 29.5% by weight, based on the weight of the dry polymer, of optional monomers, which are not non-ionic (meth) acrylic monomers, monoethylenically unsaturated, or acid monomers unsaturated monoethylenically. Optional monomers may include, for example, styrene or alkyl-substituted styrenes; butadiene; vinyl acetate, vinyl propionate or other vinyl esters; vinyl monomers, such as vinyl chloride, vinylidene chloride and N-vinyl pyrrolidone; allyl methacrylate, vinyl toluene, vinylbenzophenin, diallyl phthalate, 1,3-butylene glycol dimethacrylate, 1,6-hexanediol diacrylate and divinylbenzene. The emulsion polymer used in this invention is substantially entangled. when applied to a substrate in the method of this invention, although low levels of deliberate or accidental entanglement may be present. When low levels of pre-entanglement or gel content are desired, said low levels of optionally non-ionic, multi-ethylenically unsaturated monomers, such as, for example, from 0.1 to 5% by weight, based on the weight of the dry polymer , they can be used. However, it is important that the quality of the film formation is not materially damaged. The polymerization techniques used to prepare the acrylic emulsion polymer of this invention are well known in the art. Conventional surfactants may be used, such as, for example, anionic and / or nonionic emulsifiers, such as, for example, alkali metal or ammonium salts of alkyl, aryl or alkylaryl sulfates, sulfonates or phosphates; alkyl sulphonic acids; sulfosuccinate salts; fatty acids; monomers of ethylenically unsaturated surfactants; and ethoxylated alcohols or phenols. the amount of the surfactant used is generally 0.1 to 6% by weight, based on the weight of the monomer. A redox initiation process is used. The reaction temperature is maintained at a temperature less than 100 ° C during the course of the reaction. A reaction temperature between 30 and 95 ° C, more preferably between 50 and 90 ° C is preferred. The monomer mixture can be added in net form or as an emulsion in water. Said monomer mixture can be added in one or more additions or continuously, linearly or not, in the reaction period, or combinations thereof. The redox system includes an oxidant and a reducer. One or more oxidants, such as, for example, hydrogen peroxide, sodium peroxide, potassium peroxide, t-butyl hydroperoxide, t-amyl hydroperoxide, eumenohydroperoxide, ammonium and / or alkali metal persulfates, perborate of sodium, perfosphoric acid and its salts, potassium permanganate and ammonium or alkali metal salts of peroxydisulfuric acid, typically at a level of 0.01 to 3.0% by weight, based on the weight of the dry polymer, are used. At least one suitable reductant, such as sodium sulfoxylate formaldehyde, alkali metal and ammonium salts of sulfur-containing acids, such as sulfite, bisulfite, thiosulfate, hydrosulfite, sulfur, sodium hydrosulphide or dithionite, formadinsulfinic acid, hydroxymethanesulfonic acid, acetone bisulfite, amines such as ethanolamine, glycolic acid, glyoxylic acid hydrate, ascorbic acid, isoascorbic acid, lactic acid, glyceric acid, malic acid, 2-hydroxy-2-sulfinateacetic acid, tartaric acid and salts of the preceding acids, typically at a level of 0.01 to 3.0% by weight, based on the weight of the dry polymer, are used. The redox reaction that catalyzes the metal salts of iron, copper, manganese, silver, platinum, vanadium, nickel, chromium, palladium or cobalt can be optionally used. The oxidant and the reductant are typically added to the reaction mixture in separate streams, preferably concurrently with the monomer mixture. The polymerization is preferably carried out at a pH of from 4 to 8. In addition, a chain transfer agent, such as, for example, isopropanol, halogenated compounds, n-butyl mercaptan, n-amyl mercaptan, mercaptan n-dodecyl, t-dodecyl mercaptan, alkyl thioglycolate, mercaptopropionic acid and alkyl mercaptoalkanoate, in an amount of 0.001 to 0.05, preferably 0.0025 to 0.05 moles per kilogram of dry polymer weight, is used. C4-C22 linear or branched alkyl mercaptans, such as n-dodecyl mercaptan and t-dodecyl mercaptan are preferred. Chain transfer agents can be added in one or more additions or continuously, linearly or not, in most or all of the reaction period during limited portions of the reaction period, such as, for example, in the charge of the copper. and in the reduction of the residual monomer stage. However, at least 40% by weight, preferably at least 75% by weight, more preferably at least 95% by weight, based on the weight of the dry polymer, of the emulsion polymer, is formed by the redox polymerization , in the presence of 0.001 to 0.05 moles of the chain transfer agent per kilogram of the dry polymer weight. By "at least 40% by weight, based on the weight of the dry polymer, the emulsion polymer is formed by the redox polymerization, in the presence of 0.001 to 0.05 moles of the chain transfer agent per kilogram of the weight of the polymer. "dry polymer" is meant here that at least 40% by weight, based on the weight of the dry polymer, of the emulsion polymer, is formed by the redox emulsion polymerization and that this polymerization is carried out contemporaneously with the above presence and / or the addition of a total of 0.001 to 0.05 moles of the chain transfer agent per kilogram of the dry polymer weight. Emulsion polymerization is considered to include the modalities where some of the polymer is introduced by a polymer seeding, formed or not in itself, or formed during retention periods or formed during periods in which the monomer charge has ended and the residual monomer begins to convert to the polymer. In another aspect of the present invention, the emulsion polymer can be prepared by a multistage emulsion polymerization process, in which at least two steps differing in composition are polymerized in a sequence manner. Said process usually results in the formation of at least two mutually incompatible polymer compositions, thus resulting in the formation of at least two phases, within the polymer particles. Said particles are composed of two or more phases of various geometries, such as, for example, core / shell or core / shell particles, core / shell particles with shell phases that incompletely encapsulate the core, core / shell particles with a multiplicity of interpenetrating network particles and cores. In all those cases, the majority of the surface area of the particles will be occupied by at least one external phase and the interior of the particle will be occupied by at least one internal phase. Each of the steps of the multi-stage emulsion polymer can contain the same monomers, surfactants, redox initiation systems, chain transfer agents, etc., as described herein above for the emulsion polymer. In the case of a multi-stage polymer particle, the Tg for the purposes of this invention will be calculated by the Fox equation, as detailed herein, using the general composition of the emulsion polymer, without considering the number of steps or phases in the same. Similarly, the amounts of the composition for multi-stage polymer particles, such as, for example, the amount of the non-ionic monomer and the acidic monomer, the general composition of the emulsion polymer must be determined without considering the number of stages or phases in it. The polymerization techniques used to prepare such multi-stage emulsion polymers are well known in the art, such as, for example, U.S. Patent Nos. 4,325,856, 4,654,397 and 4,814,373. The emulsion polymer has an average particle diameter of 20 to 1000 nanometers, preferably 70 to 300 nanometers. The particle sizes herein are those determined using a Brookhaven Model BI-90 device, manufactured by Brookhaven Instruments Corporation, Holtsville NY, reported as "effective diameter". Also considered are those emulsion polymers with multimodal particle sizes, in which two or more different sizes of particles or very broad distributions are provided, as taught in U.S. Patent Nos. 5,340,858, 5,350,787, 5,352,720, 5,539,361 and 4,456,726.

The glass transition temperature ("Tg") of the emulsion polymer is typically from -20 to 100 ° C, preferably from -20 to 50 ° C, the monomers and the amounts of monomers selected to achieve the Tg range. of the desired polymer are well known in the art. The Tg used here are those calculated using the Fox equation (TG Fox, Bull, Am. Physics, Soc., Volume 1, Issue No. 3, page 1123 (1956), that is, to calculate the Tg of a copolymer of the monomers Ml and M2. 1 / Tg (cale.) = W (Ml) / Tg (Ml) + w (M2) / Tg (M2) where: Tg (cale.) Is the glass transition temperature calculated for the copolymer w (Ml) is the weight fraction of the monomer Ml in the copolymer w (M2) is the weight fraction of the monomer M2 in the copolymer Tg (Ml) is the glass transition temperature of the homopolymer Ml Tg (M2) is the glass transition temperature of the M2 homopolymer. All temperatures are in ° K.

The glass transition temperatures of the homopolymers can be found, for example, in the manual "Polymer Handbook", edited by J. Brandrup and E. H.

Immergut, Intserscience Publishers. The amount of pigment and diluent in the aqueous coating composition can vary from a pigment volume concentration (CVP) of from 0 to 85 and thus covers coatings of another form, described in the art, for example, as clear coatings, flat coatings, satin coatings, semi-gloss coatings, gloss coatings, sizing, textured coatings, and the like. The concentration in volume of the pigment is calculated by the following formula: vol. of pigment (s) + vol. of diluent (s) x 100 CVP (%) = total dry volume of paint The typical CVP of different optional levels of brightness are indicated below: The aqueous coating composition is prepared by techniques that are well known in the art of coatings. First, if the coating composition is to be pigmented, at least one pigment can be dispersed either in an aqueous medium, under high cut, such as that provided by a COWLES® mixer or, in the alternative, at least one can be used. pigment previously dispersed. Then the acrylic emulsion polymer can be added under low cut agitation together with the other auxiliary coatings as desired. Alternatively, the emulsion polymer may be present during the pigment dispersion step. The aqueous coating composition may contain conventional coating auxiliaries, such as, for example, emulsifiers, regulators, neutralizers, coalescers, thickeners or rheology modifiers, freeze-melt additives, wet edge auxiliaries, wetting agents, wetting agents , biocides, antifoaming agents, UV light absorbers, such as benzophenone, substituted benzophenones, and substituted acetophenones, dyes, waxes, and anti-oxidants. The aqueous coating composition may contain up to 50% by weight, based on the total dry weight of the polymer, of an emulsion polymer that does not meet the limitations of the emulsion polymer of the present invention, which include a polymer in emulsion that forms film and / or that does not form film. Preferably, the aqueous coating composition contains less than 5% volatile organic compounds (VOC) by weight, based on the total weight of the coating composition; more preferably the aqueous coating composition contains less than 3% VOC by weight, based on the total weight of the coating composition; even more preferably, the aqueous coating composition contains less than 1.7% VOC by weight, based on the total weight of the coating composition. A volatile organic compound ("VOC") is defined herein as a carbon-containing compound, which has a boiling point below 280 ° C at atmospheric pressure, compounds such as water and ammonia are excluded from said VOCs.

A "low VOC" coating composition is a coating composition that contains less than 5% VOC by weight, based on the total weight of the coating composition; preferably it contains between 1.7 and 0.01% by weight, based on the total weight of the coating composition. Frequently, a VOC is deliberately added to a paint or coating to improve the film properties or aids in the properties of the coating application. Examples are glycol ethers, organic esters, aromatics, ethylene- and propylene glycol and aliphatic hydrocarbons. It is preferred that the coating composition contains less than 5% by weight, based on the total weight of said coating composition of the added VOCs and more preferably less than 1.7% by weight, based on the total weight of the composition of coating of the added VOCs. Additionally, low VOC coating compositions may contain coalescing agents that are not VOC. A coalescing agent is a compound that is added to an emulsion polymer that carries water, paint or coating, and that reduces the minimum film forming temperature ("MFFT") of the emulsion polymer, paint or coating by at least 1 ° C. The MFFT is measured using the test method of ASTM D2354. Examples of a coalescence aid that is not a VOC include a plasticizer, low molecular weight polymer, and surfactants. That is, a non-VOC coalescing agent is a coalescing agent that has a boiling point above 280 ° C at atmospheric pressure. Typical methods of preparing paints or coatings can introduce accidental VOCs of the emulsion polymer, biocides, defoamers, soaps, dispersants and thickeners. They typically add 0.1% VOC by weight, based on the total weight of the coating composition. Additional methods, such as vapor separation and selection of additives containing low VOCs, such as biocides, defoamers, soaps, dispersants and thickeners, can be used to further reduce the paint or coating to less than 0.01% of the VOC by weight, based on the total weight of the coating composition. In a preferred embodiment, the aqueous coating composition has a CVP of 15 to 38 and has less than 5% VOC by weight, based on the total weight of the coating composition. In another preferred embodiment, the aqueous coating composition has a CVP greater than 38 and less than 3% VOC by weight, based on the total weight of the coating composition. In a further embodiment of the aqueous coating composition, it has a VOC of 15 to 85 and has less than 1.6% VOC by weight, based on the total weight of the coating composition. The solids content of the aqueous coating composition can be from 25 to 60% by volume. The viscosity of the polymeric aqueous composition can be from 50 KU (Krebs Units) to 120 KU, as measured using a Brookfield Digital Visor KU-1; the appropriate viscosities for different application methods vary considerably. Conventional coatings application methods, such as, for example, brush, roller and spray methods, such as, for example, air spray, air assisted spray, airless spray, low pressure spray and high volume spray, and sprayed without air, but assisted with air, can be used in the method of this invention. The aqueous coating composition can be advantageously applied to substrates, such as, for example, plastic, wood, metal, sizing surfaces, previously painted surfaces, environmentally resistant painted surfaces and cement substrates. Drying is typically carried out under ambient conditions, such as, for example, at 9 to 35 ° C. The following examples are presented to illustrate the invention and the results obtained by the testing procedures.

Test Procedures Resistance to Scouring: A coating composition and a comparative composition, with the same volume of solids as the coating composition, were applied on a simple graph of black vinyl. The compositions were applied in such a way that two compositions were placed side by side and applied together by a Bird film application device of 0.0762 mm 152.4 mm wide. Each composition formed a coating with a width of 7.6 cm on a simple graph, and the two compositions had the same coating thickness. The sample was allowed to dry at 23 ° C and 50% relative humidity for 7 days. The resistance to abrasive scouring was measured with a scouring machine (Gardner Abrasive Tester), which uses 10 g of the abrasive medium and 5 ml of water. A piece of 0.0254 mm thick, 76.2 mm wide vinyl sheet was placed below the sample vinyl chart. The two lateral edges of the sheet were in the center of each coating. The number of cycles in the first zone of each removed coating was recorded. Resistance to scrubbing was reported as a percentage of the number of cycles of the coating composition versus the comparative composition.

Alkali Resistance - Loss of Gloss The sample preparation and drying / conditioning were as for the previous test of resistance to scrubbing. Glosses were measured at both 20 and 60 degrees for each sample, using a Glossmeter device (BYK-Garner). The sample panel was scrubbed with a machine (Gardner Abrasive Tester) using an abrasion can of 454 g, specially prepared. Said abrasion canister was wound with a block of sparse fabric having initial dimensions of 230 mm x 150 mm, and which was folded twice to form a block of 57 mm x 150 mm. The thin cloth block was saturated with 1% of the Tide detergent solution. The sample panel was first rubbed for 250 cycles; then the block was re-saturated with 1% of the Tide solution and the panel was rubbed for an additional 250 cycles. The sample panel was thoroughly rinsed and dried for 24 hours at room temperature. The brightness at both 20 and 60 degrees was measured again for the sample panel. The loss of brightness was determined by the percentage of brightness change, before and after the treatment with the detergent solution Tide.

Hydrolytic Stability: The sample preparation and drying / conditioning were like the resistance test to the previous scrubbing. The graph of each composition was cut into strips of 25.4 mm x 50.8 mm and weighed. A sample strip was placed in a 60 ml glass jar containing 25 g of a 0.5 N NaOH solution. Approximately half of the sample strip was immersed in the NaOH solution. After 48 hours, the sample strip was removed and rinsed thoroughly with water. The sample strip was dried for 24 hours and weighed again. The percentage of the weight loss of the sample strip was recorded. A visual evaluation of the sample was also made. The abbreviations listed below were used in all the examples. MAA = methacrylic acid BA = butyl acrylate MMA = methyl methacrylate VA = vinyl acetate n-DDM = n-dodecyl mercaptan SLS = sodium lauryl sulphate (28% active) APS = ammonium persulphate water DI = deionized water COMPARATIVE EXAMPLES A-D. Preparation of the emulsion polymers. The monomers for each example (Table CE-1) were combined with 455 g of DI water, 6.9 g of sodium carbonate and 30.5 g of SLS and emulsified with stirring. 5.2 g of SLS and 400 g of DI water were charged to a 3-liter multi-necked flask, equipped with a mechanical stirrer. The contents of the flask were heated to 85 ° C under nitrogen. To the stirred contents of the copper were added 35 g of the monomer emulsion, followed by 3.5 g of APS in 10 g of DI water. 30 g of a 50% solution of ureido methacrylate were added to the remainder of the monomer emulsion and the gradual addition of the monomer emulsion was subsequently initiated. The total addition time for the monomer emulsion was 90 to 100 minutes. The temperature of the reactor was maintained at 83 ° C throughout the polymerization. 20 g of DI water were used to rinse the emulsion charge line to the reactor. After completing the addition of monomer emulsion, the reactor was cooled to 60 ° C. 10 ppm of ferrous sulfate, 1 g of t-butyl hydroperoxide and 0.5 g of D-isoascorbic acid in aqueous solutions were added. The polymer emulsion was neutralized to a pH of 9 to 10 with ammonium hydroxide.

Table CE-1 - Monomer Charges for Comparative Examples A-D.

Table CE-2 - Physical Properties of Comparative Examples A-D.

Notes: Particle size was determined by the BI-90 Particle Sizer from Brookhaven Instruments Total solids determined by weight loss after 30-45 minutes at 150 ° C. Viscosity determined using the Viscometer @ 60 rpm, from Brookfield LVTD.

EXAMPLES 1-3 and COMPARATIVE EXAMPLE E. Preparation of acrylic emulsion polymers. The monomers for each example (Table 1-1) were combined with 400 g of DI water, 6.9 g of sodium carbonate and 30.5 g of SLS and emulsified with stirring. 5.2 g of SLS and 380 g of DI water were charged to a 3-liter multi-necked flask equipped with a mechanical stirrer. The contents of the flask were heated to 65 ° C under nitrogen. To the stirred contents of the copper were added 35 g of the monomer emulsion followed by 0.01 g of ferrous sulfate heptahydrate and 0.02 g of the tetrasodium salt of ethylenediamine-tetraacetic acid in 15.6 g of DI water. Polymerization was initiated by the addition of 0.54 g of APS in 8 g of DI water, followed by 0.27 g of sodium hydrosulfite in 8 g of DI water. 30 grams of a 50% solution of ureide methacrylate were added to the remainder of the monomer emulsion and the gradual addition of the monomer emulsion was subsequently initiated. The separate solutions of 2.9 g of APS in 50 g of DI water and 1 g of D-isoascorbic acid in 50 g of DI water were fed concurrently with the monomer emulsion. The total addition time for the three charges was 90-100 minutes. The temperature of the reactor was maintained at 65 ° C throughout the polymerization. 20 g of DI water was used to rinse the emulsion charge line to the reactor. After completing the addition of the monomer emulsion, the reactor was cooled to 60 ° C. 10 ppm of ferrous sulfate, 1 g of t-butyl hydroperoxide and 0.5 g of D-isoascorbic acid in aqueous solutions were added. The polymer emulsion was neutralized at a pH of 9 to 10, with ammonium hydroxide.

Table 1-1 - Monomer Charges for Examples 1-3 and Comparative E.

Table 1-2 - Physical Properties of Examples 1-3 and Comparative E.

Notes: Particle size was determined by the BI-90 Particle Sizer from Brookhaven Instruments Total solids determined by weight loss after 30-45 minutes at 150 ° C. Viscosity determined using the Viscometer @ 60 rpm, from Brookfield LVTD.

EXAMPLE 4 - Formation of Aqueous Coating Compositions All aqueous coating compositions were obtained using the following formulation: Material Grams Propylene Glycol 18.2 Pigment Dispersant (TAMOL ™ 731) 6.45 Defoamer (FOAMASTER VL) 0.5 Titanium Dioxide (Ti-PURE ™ R-900) 126.50 Water 31.0 The above ingredients were mixed in a high cut Cowles mixer and then the following ingredients were added with a low cutting mixture: Emulsion polymer 232.29 Opaque polymer (ROPAQUE ™ ULTRA) 14.40 Coalescent (TEXANOL ™) 4.83 Defoamer (FOAMASTER ™ VL) 0.5 Rheology Modifier (ACRYSOL ™ RM-120) 14.2 Rheology Modifier (ACRYSOL ™ RM-825) 0.25 Water 77.79 Note: TAMOL, ROPAQUE and ACRYSOL are trademarks of Rohm and Haas Company. FOAMASTER is a trademark of Henkel Corp. TI -PURÉ is a trademark of The DuPont Nemours. Col. TEXANOL is a trademark of Eastman Chemical Co. These aqueous coating compositions contain 4.4% VOC by weight, based on the total weight of the coating composition.

EXAMPLE 5. Evaluation of the resistance to scrubbing of dry coatings. Aqueous coating compositions were prepared, according to Example 4, as with the emulsion polymers of Examples 1-3 and Comparative Examples A-E. The dried film of each aqueous coating composition was evaluated for the scrub resistance; the results are presented in Table 5-1.

Table 5-1 - Results of the resistance to scrubbing The dry film of the aqueous coating composition, which contains the emulsion polymer of Example 1 of this invention, provides superior scouring resistance to that of the corresponding composition containing the emulsion polymer of Comparative Example B. The dry film of the aqueous coating composition, containing the emulsion polymer of Example 2 of this invention, provides superior scouring resistance to that of the corresponding composition of Comparative Example C. The dry film of the aqueous coating composition, which contains the polymer In the emulsion of Example 3 of this invention, it provides a scrub resistance superior to that of the corresponding composition of Example Comparative D. The dried films of the aqueous coating compositions, which contain the emulsion polymer of Examples 1 and 2 of this invention, provide a substantially superior scrub resistance to that of the compositions of Comparative Examples A-E.

EXAMPLE 6. Evaluation of Alkali Resistance - Loss of Brilliance Aqueous coating compositions were prepared, according to Example 4, incorporating the aqueous emulsion polymers of Examples 1 and 2 and Comparative Example F, an emulsion polymer of (74.8 VA / 24.8 BA / 0.4 acid). A dry film of the three compositions was prepared on a simple graph of black vinyl and the Alkali Resistance - Loss of Brightness was determined. The results are presented in Table 6-1.

Table 6.1 - Evaluation of alkali resistance The dried films of the aqueous coating compositions, which contain the aqueous acrylic emulsion polymers of Examples 1 and 2 of this invention, exhibited no loss of gloss and thus passed the test.

EXAMPLE 7 - Evaluation of Hydrolytic Stability Aqueous coating compositions were prepared, according to Example 4, incorporating the aqueous emulsion polymers of Examples 1 and 2, and Comparative Example F, a p-emulsion polymer (74.8 VA / 24.8 BA / 0.4 acid). A dry film of the three compositions was prepared on a simple graph of black vinyl and the Hydrolytic Stability was determined. The results are presented in Table 7-1.

Table 7-1 - Evaluation of hydrolytic stability EXAMPLE 8 AND COMPARATIVE EXAMPLE G - Preparation of acrylic emulsion polymers The monomers of Comparative Example G (Table 8-1) were combined with 455 g of DI water, 6.9 g of sodium carbonate and 30.5 g of SLS and emulsified, with agitation. 5.2 g of SLS and 400 g of DI water were charged to a 3-liter multi-necked flask equipped with a mechanical stirrer. The contents of the flask were heated to 85 ° C under nitrogen. To the stirred contents of the copper were added 35 g of an emulsion of monomers, followed by 3.5 g of APS in 10 g of DI water. 30 g of a 50% solution of ureido methacrylate were added to the remainder of the monomer emulsion and the gradual addition of an emulsion of monomers was subsequently initiated. The total addition time for the monomer emulsion was 90 to 100 minutes. The temperature of the reactor was maintained at 83 ° C throughout the polymerization. 20 g of DI water was used to rinse the emulsion charge line to the reactor. After completing the addition of the monomer emulsion, the reactor was cooled to 60 ° C, 10 ppm of ferrous sulfate, 1 g of t-butyl hydroperoxide and 0.5 g of D-isoascorbic acid in aqueous solutions were added. The polymer emulsion was neutralized to a pH of 9-10 with ammonium hydroxide.

The monomers of Example 8 (Table 8-1) were combined with 400 g of DI water, 6.9 g of sodium carbonate and 30.5 g of SLS and emulsified, with stirring. 5.2 g of SLS and 380 g of DI water were charged to a 3-liter multi-necked flask equipped with a mechanical stirrer. The contents of the flask were heated to 65 ° C under nitrogen. At the stirred contents of a copper there was added 35 g of a monomer emulsion, followed by 0.02 g of ferrous sulfate heptahydrate and 0.02 g of the tetrasodium salt of ethylenediamine-tetraacetic acid in 15.6 g of DI water. Polymerization was initiated by the addition of 0.54 g of APS in 8 g of DI water, followed by 0.27 g of sodium hydrosulfite in 8 g of DI water. 30 g of a 50% solution of ureido methacrylate was added to the remainder of the monomer emulsion and the gradual addition of the monomer emulsion was subsequently initiated. Separate solutions of 2.9 g of APS in 50 g of DI water and 1 g of D-isoascorbic acid in 50 g of DI water were fed concurrently with the monomer emulsion. The total addition time for the three charges was 90-100 minutes. The temperature of the reactor was maintained at 65 ° C throughout the polymerization. 20 g of DI water were used to rinse the emulsion charge line to the reactor. After completing the addition of the monomer emulsion, the reactor was cooled to 60 ° C. 10 ppm of ferrous sulfate, 1 g of t-butyl hydroperoxide and 0.5 g of D-isoascorbic acid were added in aqueous solutions. The polymer emulsion was neutralized to a pH of 9-10 with ammonium hydroxide.

Table 8-1 - Monomer Charges EXAMPLE 9 - Formation of Aqueous Coating Compositions The Grinding Premix was obtained using the ingredients in the ratios of Table 9.1 and mixed in a high speed Cowles disperser for 20 minutes. A portion of the Grinding Premix that contained the ingredients in the amounts listed in Table 1 was transferred to another container for each paint and the Dilution ingredients were added under low speed mixing in the given order. The concentration in final volume of the pigment for each painting was 19% and the solids in volume were 36%. The VOCs of the aqueous coating compositions were 0.1% by weight, based on the total weight of the coating composition.

Table 9.1 - Aqueous coating composition Note: SURFYNOL is a trademark of Air Products and Chemicals Inc .: TEGO is a trademark of Tego CEIME Service. A scour test was performed on two specimens of each example, following the procedure outlined in the test method of ASTM D2486-00 with the following exceptions: A Bird applicator of 76 micron film was used to apply the paints, and the specimens of test kept on each side of the sheet halfway between the sheet and the end of the specimen, directly, holding rather than by means of a frame with packing, as delineated in the ASTM D2486 standard. Method A of the test method was followed differently. The data obtained are given in Table 9.2 Table 9.2 - Results of the scrub resistance test, Cycles to fail The dry film of the aqueous coating composition, which contains the emulsion polymer of Example 8 of this invention, provides a superior resistance to scrubbing than that of the corresponding composition containing the emulsion polymer of Comparative Example H.

Claims (1)

1. CLAIMS 1. An aqueous acrylic emulsion polymer, which comprises, as copolymerized units: from 70 to 99.5% by weight, based on the weight of the dry polymer, of a (meth) acrylic, nonionic, monoethylenically unsaturated monomer, and from 0.3 to 10% by weight, based on the weight of the polymer, of a monoethylenically unsaturated acid monomer, wherein at least 40% by weight, based on the weight of the dry polymer, of said emulsion polymer, is formed by the redox polymerization, in the presence of 0.001 to 0.05 moles of a chain transfer agent per kilogram of the dry polymer weight. The acrylic emulsion polymer of claim 1, wherein said redox polymerization is carried out in the presence of 0.025 to 0.025 moles of the chain transfer agent per kilogram of dry polymer weight. The acrylic emulsion polymer of claim 1, wherein said redox polymerization is carried out at a pH of 4 to 8. 4. An aqueous coating composition, comprising an aqueous acrylic emulsion polymer, said polymer comprises, as units copolymerized, from 70 to 99.5% by weight, based on the weight of the dry polymer, of a monoethylenically unsaturated (meth) acrylic monomer and from 0.3 to 10% by weight, based on the weight of the dry polymer , of a monoethylenically unsaturated acid monomer, in which at least 40% by weight, based on the weight of the dry polymer, of said emulsion polymer is formed by the redox polymerization, in the presence of 0.001 to 0.05 moles of a chain transfer agent, per kilogram of dry polymer weight. The aqueous coating composition of claim 4, wherein said redox polymerization is carried out in the presence of 0.0025 to 0.025 moles of the chain transfer agent per kilogram of the dry polymer weight. 6. The aqueous coating composition of claim 4, having a pigment volume concentration of 15 to 38 and having an amount of volatile organic compounds of less than 5% by weight, based on the total weight of the composition of the composition. covering. The aqueous coating composition of claim 4, wherein the volume concentration of the pigment is greater than 38 and with volatile organic compounds less than 3% by weight, based on the total weight of the coating composition. The aqueous coating composition of claim 4, which has a pigment volume concentration of 15 to 85 and a content of volatile organic compounds of less than 1.7% by weight, based on the total weight of the coating composition . 9. A method for improving the resistance to scrubbing of a dry coating, said method comprises: a) forming an aqueous coating composition, comprising an aqueous acrylic emulsion polymer, said polymer includes, as copolymerized units: from 70 to 99.5% by weight, based on the weight of the dry polymer, of a monoethylenically unsaturated (meth) acrylic monomer and from 0.3 to 10% by weight, based on the weight of the dry polymer, of a monoethylenically unsaturated acid monomer , wherein at least 40% by weight, based on the weight of the dry polymer, of the emulsion polymer is formed by the redox polymerization, in the presence of 0.001 to 0.05 moles of a chain transfer agent per kilogram of the weight of the dry polymer; b) applying said coating composition to a substrate; and c) drying, or allowing to dry, said applied coating composition. The method of claim 9, wherein said redox polymerization is carried out in the presence of 0.001 to 0.05 moles of the chain transfer agent per kilogram of the dry polymer weight.